In real-world conditions, it is likely
that the improper use of sunscreen and/or increased exposure
time results in production of vitamin D among sunscreen
users.71 The FDA standard for application of sunscreen is 2
mg/2 cm. Actually, 25% to 50% of that amount is applied.
This results in a protection factor of 8 to 15 when using a
sunscreen labeled 30 FPS